package algorithm.sort;

/**
 * 快排
 */
public class QuickSort {
    public void sort(int[] arr, int l, int r) {
        if (l < r) {
            int[] p = partition(arr, l, r);
            sort(arr, l, p[0] - 1);
            sort(arr, p[1] + 1, r);
        }
    }

    public int[] partition(int[] arr, int l, int r) {
        swap(arr,l + (int) (Math.random() * (r - l + 1)),r);
        int less = l - 1;
        int more = r;
        while (l < more) {
            if (arr[l] < arr[r]) {
                swap(arr, ++less, l++);
            } else if (arr[l] > arr[r]) {
                swap(arr, --more, l);
            } else {
                l++;
            }
        }
        swap(arr, more, r);
        return new int[]{less + 1, more};
    }

    public void swap(int[] arr, int i, int j) {
        arr[i] = arr[i] ^ arr[j];
        arr[j] = arr[i] ^ arr[j];
        arr[i] = arr[i] ^ arr[j];
    }
}
